﻿function selectNumber(i)
{
    document.getElementById("txtNhap").value += i;
}
function cancel()
{
    document.getElementById("txtNhap").value = null;
}
function clearNumber()
{
    var a = document.getElementById("txtNhap").value;
    var b = a.substr(0, (a.length - 1));
    document.getElementById("txtNhap").value = b;
}